1. Field of the Invention
The present invention relates to laser radar systems, and more particularly, to correcting the angular drift of laser radar systems.
2. Background
Laser Radar systems, among other emerging technologies, require an elevation, azimuth scanner. One of the common and inexpensive alternatives is the galvanometric x y scanner. This scanner is composed of a pair of mirrors each rotated by galvanometric motors about axes that are approximately horizontal and roughly perpendicular to each other. A light beam entering the scanner is reflected from a first mirror onto second mirror in such a way that rotation of the first mirror rotates the beam in azimuth and the second mirror rotates the beam in altitude.
Measurement of the angle of the mirrors is currently done with a capacitive or optical sensor mounted on the galvanometric motor. Both of these sensors have significant calibration drifts with temperature. For a laser radar system operating at a large distance, the angular resolution of the scanner is the limiting factor in the three dimensional accuracy. For example, consider laser radar with a maximum range of 10 meters. If we want a position resolution of 25 microns, then the angular resolution must be 2.5 microradians. Typical drifts in the angular accuracy over time are many times this figure.
This problem has been partially solved by the use of fiducial targets. Fiducial targets are objects mounted in the field of view of the xy scanner which are periodically measured to correct for the angular drift in the galvanometric motors. This solution is not suited for many applications of laser radar systems. For example, the solution would not be suited in measuring articles on a manufacturing floor or assembly line, because setting out the fiducial targets is an extra step in the measurement process and the targets would be in the way of the assembly technicians.
Therefore, there is a need for a method and system for correcting the angular drift of radar systems using internal fiducials.